A number of ceramic yarns having a resistance to extremely high temperatures have been developed in recent years. Although advantageous because of their high temperature resistance, inertness, dimensional stability, etc., they are typically very brittle, that is, the yarn has a very limited ability to withstand bending stresses. A ceramic yarn having a particularly high resistance to temperature is that made of alumina-boria-silica fibers which are resistant to temperatures of up to about 1430.degree. C. These alumina-boria-silica fibers are disclosed in U.S. Pat. Nos. 3,795,524 and 4,047,965, with the alumina-boria mol ratio generally being between 3:1 and 24:1.
Brittle high temperature yarns have been incorporated into sewing threads, as disclosed in U.S. Pat. Nos. 4,375,779 and 4,430,851. These high temperature resistant sewing threads can be used to sew together high temperature fabrics to produce an article which is resistant to very high temperatures. However, such high temperature sewing threads are not adapted to use in different types of textile processes such as stitchbonding or knitting operations, which are desired processes for making useful high temperature resistant fabrics. The existing sewing threads are too stiff to be useful in commercially available stitchbonding or knitting machines, as they will not conform to the needles in stitchbonding machines and are too heavy to be used in fine-gauge knitting machines. Further, stitchbonding and knitting machines exert high stresses at short radius bends on the yarns used, and brittle ceramic yarns break when used on such machines. The result has been that brittle ceramic yarns have generally been foreclosed from use in stitchbonded and knitted fabrics.